Abstract African Americans (AAs) have a greater risk for poor cognitive aging compared to White Americans, whether measured as clinical dementia or as lower cognitive function in late life. Identification of modifiable risk factors for Alzheimer?s Disease and related dementias (ADRD) is a key public health goal, given the rising number of older adults, the lack of effectiveness of disease-modifying therapies thus far, and the incredible emotional, psychological, and financial toll dementia exacts on patients and their families. Assessment of risk and resilience factors that may be particularly relevant to AA communities is of increasing public health significance. Research indicates that AA disparities in ADRD risk may emerge earlier in life; however, prior research on disparities in cognitive decline and ADRD have largely focused on adults after the age of 65. Therefore, assessment of modifiable risk factors for dementia in midlife AAs is imperative. At the same time, ambient air pollution is an emerging modifiable risk factor for dementia with wide opportunity for exposure over the life course. In particular, AAs are disproportionately exposed to air pollution compared to other groups, and such exposure is often coupled with neighborhood and economic deprivation, which can increase stress and heighten susceptibility to pollutant exposures. In response to NOT-CA-20-019, this administrative supplement proposes to add novel, spatially-refined longitudinal measures of air pollution exposure to our ongoing NCI- funded study (CA149105) that is following a cohort of mid- to late-life AAs residing in two low-income neighborhoods in Pittsburgh and to study the association between air pollution exposure and cognitive outcomes and ADRD risk. The parent study is focused on neighborhood change and dietary outcomes among residents over time, and a prior administrative supplement allowed for our team to add measures of cognitive function. This proposed supplement will allow for clinical adjudication of Mild Cognitive Impairment (MCI) and dementia in a sample of participants from this cohort and build on the parent study?s (CA149105) rich existing data, which includes repeated measures of individual and contextual factors from 2011 through 2020. Aims of this proposal include: (1) quantifying the association between chronic exposure to air pollution and cognitive function and clinical cognitive outcomes (MCI and dementia); (2) examining the role of key individual-level factors (socioecoconomic status, perceived stress, body mass index) as potential modifiers in this association; (3) evaluating whether key neighborhood-level conditions (neighborhood socioeconomic conditions, residential and commercial investments) exacerbate or mitigate the association. The proposed supplement represents a unique and timely opportunity to expand the scope of the parent R01 to examine the relationship between air pollution and cognitive outcomes and ADRD risk in a sample of low-income, mid-life AA adults; a population burdened by multiple environmental and social stressors which collectively may contribute to disproportionate risk for cognitive decline and ADRD.